1. Field of the Invention
The present invention relates to condition monitoring of batteries generally and, more particularly, but not by way of limitation, to novel condition monitoring of opportunity charged batteries in which the battery condition monitor is disconnected from the battery during charging.
2. Background Art
Conventionally, batteries for battery-powered vehicles have been given relatively long charging periods at regular intervals. A prime example of the type of vehicle with which this procedure is used is the battery-powered forklift truck which may be used for a working shift and then taken xe2x80x9coff-linexe2x80x9d for a shift while the battery is charged or the discharged battery on the forklift truck is replaced with a fully charged battery. This is generally the optimum charging arrangement for the battery. Additionally, ideally, but practically usually separated from the battery, a battery condition monitor, or xe2x80x9cfuel gagexe2x80x9d remains attached to the battery so that it continues to monitor the condition of the battery while charging is taking place.
Recently, there has been a proliferation of small battery-powered vehicles such as small battery-powered pallet trucks, lifts, and hand carts in such varied applications as grocery stores and lumber yards. Often, these replace manually operated vehicles, in order to provide a more xe2x80x9cworker friendlyxe2x80x9d environment or to comply with laws regulating how much a worker can be required to lift. Because the use of such vehicles is less structured than the use of larger battery-powered vehicles, it is common to employ xe2x80x9copportunity chargingxe2x80x9d in which the battery is connected to a (usually) off-board charger, in a relatively time-unrelated manner, whenever the vehicle happens not to be in use for a period of time. In addition, the battery should periodically be fully charged. The battery is dedicated to a given vehicle and remains in place in the vehicle during charging, with the battery cable being disconnected from the vehicle and connected to the charger, thus removing power from the battery condition monitor and, consequently, presenting the monitor with a period in which it cannot monitor the condition of the battery.
There are several reasons a battery condition monitor may be disconnected: (1) merely for safety, with no charging or discharging, (2) to take advantage of an opportunity charge, (3) to put the battery on full charge as opposed to opportunity charging, (4) unintended system electrical intermittents or circuit breaker/fuse interruptions, (5) tampering or sabotage to xe2x80x9cfoolxe2x80x9d the instrumentation so that the monitor indicates more or less than actual battery capacity, and/or (6) cost considerations precluding the addition of the necessary wiring and interconnections to keep the battery condition monitor operationally connected to the battery at all times. In any case, the monitor (if not manually reset after a full charge) must determine what happened to the battery during the period of disconnect.
Opportunity charging has been adequately addressed in numerous applications where a battery state-of-charge monitor is continuously connected to the battery. Some patents which generally describe such systems include: U.S. Pat. No. 4,012,681, issued Mar. 15, 1977, and titled BATTERY CONTROL SYSTEM FOR BATTERY OPERATED VEHICLES; U.S. Pat. No. 4,288,734, issued Sep. 8, 1981, and titled BIDIRECTIONAL INTEGRATOR; and U.S. Pat. No. 4,740,754, issued Apr. 26, 1988, titled BIDIRECTIONAL BATTERY STATE-OF-CHARGE MONITORxe2x80x9d.
Some other patents which describe such systems and which require relatively precise relaxation characterization and very high accuracy and resolution in measurement include: U.S. Pat. No. 4,388,618, issued Jun. 14, 1983, and titled BATTERY STATE OF CHARGE INDICATOR OPERATING ON BIDIRECTIONAL INTEGRATIONS OF TERMINAL VOLTAGE; U.S. Pat. No. 4,460,870, issued Jul. 17, 1984, and titled QUIESCENT VOLTAGE SAMPLING BATTERY STATE OF CHARGE METER; and U.S. Pat. No. 4,514,694, issued Apr. 30, 1985, and titled QUIESCENT BATTERY TESTING METHOD AND APPARATUS.
Some additional patents which describe battery state of charge monitoring systems include U.S. Pat. No. 4,017,724, issued Apr. 12, 1977, and titled APPARATUS FOR MEASURING BATTERY DEPLETION BY MONITORING REDUCTIONS IN VOLTAGE; U.S. Pat. No. 4,193,026, issued Mar. 11, 1980, and titled METHOD AND APPARATUS FOR MEASURING THE STATE OF CHARGE OF A BATTERY BY MONITORING REDUCTIONS IN VOLTAGE; U.S. Pat. No. 4,560,937, issued Dec. 24, 1985, and titled BATTERY STATE OF CHARGE METERING METHOD AND APPARATUS; and U.S. Pat. No. 5,451,881, issued Sep. 19, 1995, and titled METHOD AND MEANS FOR ADJUSTING BATTERY MONITOR BASED ON RATE OF CURRENT DRAWN FROM THE BATTERY.
The disclosures of the foregoing patents are incorporated by reference hereinto.
Accordingly, it is a principal object of the present invention to provide a method of monitoring battery condition in situations in which the battery condition monitor may be disconnected from the battery for a period of time, the method including computing battery charge restoration through implication whenever the battery has been disconnected from the battery condition monitor.
A further object of the present invention is to provide such a method which employs a knowledge set including: (1) an approximate characterization of the battery""s relaxation response, (2) an approximate characterization of the charging response of the battery and battery charger combination, (3) knowledge of the battery""s computed state-of-charge at the moment of disconnection of the monitor from the battery, (4) knowledge of the real time at the moment of disconnection of the monitor from the battery, (5) knowledge of the real time at the moment of reconnection of the monitor to the battery, and/or (6) knowledge of the battery""s voltage at the moment of reconnection of the monitor to the battery.
An additional object of the present invention is to provide such a method that provides an estimate of the length of disconnection time during which the battery was charged.
Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures.
The present invention achieves the above objects, among others, by providing, in a preferred embodiment, a method of condition monitoring of an opportunity charged battery, comprising: (a) determining length of time said battery has been off-line; (b) determining whether charging of said battery has occurred during said length of time; (c) if step (b) results in a determination that said charging of said battery has occurred, determining degree of charging of said battery occurring during said length of time; and (d) if step (b) results in a determination that charging of said battery has occurred, resetting a condition monitor associated with said battery to reflect said degree of charging of said battery.